Hygroscopicity and thermodynamic properties of grains of Moringa oleifera L.

Knowledge of the movement of water molecules inside material is important for the study of interactions between water and chemical components of agricultural products. The thermodynamic properties calculation reports this need, being the source of information to design drying equipment, calculate the energy required in this process and evaluate the physical phenomena that occur on the food surface. Given the importance of the subject, the objective of this study was to determine the thermodynamic properties of the water desorption process in lettuce seeds. Lettuce seeds had an initial moisture content of 9.3% (d.b.). The equilibrium moisture content of seeds was determined by static gravimetric method at different temperatures (10, 20, 30, 40 and 50 ± 1 °C) and relative humidity values (between 11 and 96%). Experiments were conducted in triplicate. It was observed that, with increasing equilibrium moisture content, there was a reduction in the energy required for evaporation of water in lettuce seeds, with values of integral isosteric heat of desorption in the water content range 2.1 to 21.2% (d.b.) which varied from ‘4164.89 to 2477.43’ kJ kg-1. With increasing equilibrium moisture content there was a decrease in differential entropy, resulting in lower demand for mobility of water molecules. The Gibbs free energy also decreased with increasing equilibrium moisture content and was positive for all temperatures studied, showing non-spontaneity of water desorption in the seeds. The enthalpy-entropy compensation theory was has been satisfactorily applied to the sorption phenomenon and the water desorption process in lettuce seeds was controlled by enthalpy.

Solanum gilo is a plant belonging to the family Solanaceae with a probable origin in Africa. It was introduced to Brazil by workers. The fruit is cultivated by small producers in Brazil and it is a source of food for the low-income population. Its seeds are harvested with high moisture contents, and the drying process is necessary. Sorption isotherms consist of the relation between water activity (aw) and moisture content of an agricultural product at a constant temperature. This information contributes to the drying process, thus favoring an increased longevity of agricultural products, such as seeds. This research aims to determine the desorption isotherms of Solanum gilo seeds and calculate their thermodynamic properties (enthalpy, entropy and Gibbs free energy). Sorption experiments were performed by the gravimetric static method using saline solutions. Several mathematical models were fitted to the experimental data, and the selection of the best model was performed by statistical criteria. Equilibrium moisture contents were obtained at 10, 20 and 30°C and at water activities between 0.111 and 0.985 (decimal). The modified Oswin model best represents moisture desorption isotherms of Solanum gilo seeds under the studied conditions. The energy required for the process was 0.22-555.68 kJ kg-1. The latent heat of vaporization (L), the enthalpy (Qst), the entropy (ΔS) and the Gibbs free energy (ΔG) increased with the reduction of the equilibrium moisture content of seeds. The theory of isokinetics is valid for the desorption process.

The study of the thermodynamic properties provides the knowledge of the sorbent affinity by the water and the spontaneity of the sorption process, important to design drying equipment and to predict hygroscopic behavior during storage. This work aimed to determine and evaluate isotherms of hygroscopic equilibrium and thermodynamic properties for different equilibrium conditions (water contents and temperatures) in sunflower seeds, using the indirect static method. Sunflower seeds with initial water content of 0.164 (decimal, dry basis - d.b.) were used. Fifteen mathematical models were tested for hygroscopic equilibrium modeling, and the Smith model presented the best fit. It was verified that the thermodynamic properties were influenced by the water content, the integral isosteric desorption heat increased with the decrease of the equilibrium water content, ranging from 1.787 to 2.670 kJ kg-1 to 0.198 to 0.0518 (decimal, d.b.), respectively, the desorption process of the sunflower seeds was controlled by the enthalpy and the Gibbs free energy, which varied from 3.6363 to 200.1730 kJ kg-1, was positive for the temperatures studied, with increase to during the desorption process, proving to be a non-spontaneous process.

To maintain seed and soil quality of pumpkin, energy knowledge associated with processing and storage stages is strategic for the optimization of the thermodynamic processes needed for product stabilization. Thus, the objective of this study was to determine isosteric heat, differential entropy, and Gibbs free energy within a temperature range from 20 to 70° C, and relative air humidity levels between 10.75 and 85.11%. The study was based on empirical data for water activity determination. As a result, we verified that as moisture content decreased, the integral isosteric heat of the product increased from 2502.35 to 6231.17 kJ kg-1, differential entropy raised from 1.18 to 12.43 kJ kg-1 K-1, and Gibbs free energy ranged from -243.84 to -432.59 kJ kg-1. Thus, we concluded that the lower the water availability in seeds, the greater the energetic requirement for its removal, as there is a major interaction between water and the product (seeds), indicating an increasingly less spontaneous desorption process.

Pigeon pea is a common plant cultivated in family farming.It is often used as a source of protein for animal breeding.The knowledge of the drying kinetics and the thermodynamic properties of pigeon pea beans (Cajanus cajan) is relevant for simulation of drying, which aims to maintain the quality of beans.The objective of this study is to estimate the drying curves of pigeon pea beans using mathematical models.This study also aims to determine their thermodynamic properties.Forced-drying greenhouses were used for the drying process.The initial water content of pigeon pea beans was 1.00 dry basis (db).Beans were weighed periodically until reaching a near equilibrium water content.Ten mathematical models were fitted to experimental data to characterize drying processes using the following statistical criteria: coefficient of determination (R²), mean relative error (P), mean standard error (SE), chi-square (χ²), and residue distribution.From the selected model and the Arrhenius equation, the effective diffusion coefficient and the activation energy used for the calculation of the enthalpy, entropy and Gibbs free energy were obtained.The Midilli was the best model to represent the kinetics of drying of pigeon pea beans.The increase in drying air temperature increases Gibs free energy and diffusivity, decreases enthalpy, and maintains the entropy negative.

In this study, adsorption isotherms of freeze‐dried mahaleb powder were obtained using gravimetric method at four different temperatures (5, 25, 35, and 60°C). Experimental adsorption data were modeled using empirical models and artificial neural network. The GAB model gave the best fit among the empirical models with high R2 (0.9908–0.9982) and low P% (4.71–8.40%) values. However, artificial neural network (ANN) model having 10 hidden neurons optimized using Lavenberg‐Marquardth training algorithm was superior to the empirical models with the highest R2 (0.9965–0.9999) and lowest P% (0.74–8.52%) values. The ANN model explained the adsorption behavior of mahaleb powder ideally at all temperatures. In addition to the adsorption kinetics of mahaleb powder, thermodynamic properties such as isosteric heat of sorption, differential entropy and Gibbs free energy were also determined. Isosteric heat of sorption values were high when moisture contents of the powders were low. Also, differential entropy values followed the same trend which indicated that the adsorption process was driven by enthalpy. Gibbs free energy at the isokinetic temperature of 458.48 K was determined as −306.7 J/mol. Gibbs free energy values were below zero at all different temperatures. The results showed that ANN model can be suitable for predictive control systems in the food industry and the data obtained for thermodynamic properties can be useful for the storage of mahaleb powder in industrial scale.Practical ApplicationsAn intelligent model, which is artificial neural network was used for modeling of adsorption behavior of freeze‐dried mahaleb powder and it predicted the adsorption data better than empirical models. Thermodynamic properties which are mostly important for the prediction of energy consumption of a process were also determined. The data of the freeze‐dried mahaleb powder can be significant for the food industry in terms of prediction of shelf‐life and energy requirements.

The objective of the present work was to determine desorption isotherms of okra seeds for diverse conditions of temperature (10C to 50C) and relative humidity (0.11 to 0.96) of the air, as well as determine the values of isosteric heat of desorption, differential entropy, and Gibbs free energy. To obtain the equilibrium moisture content, a static method was used. Experimental data were adjusted to frequently used mathematical models for representation of hygroscopicity of agricultural products. Calculation of the net isosteric heat of desorption was performed based on the Clausius-Clapeyron thermodynamic relation. From the obtained results, it was concluded that equilibrium moisture content of the okra seeds decreased with an increase in temperature at the same relative humidity, as is the case of the majority of agricultural products. Based on statistical parameters, the Chung-Pfost model best represented the hygroscopicity of the okra seeds. Values of the integral isosteric heat of desorption as well as the differential entropy and Gibbs free energy for the okra seeds decreased with an increase in moisture content.

Studies about the thermodynamic properties of ryegrass seeds are necessary to improve post-harvest processes, relating the factors that affect product quality with the interaction between water and its chemical components. Given the importance of recognizing and understanding the intrinsic behavior of water in ryegrass seeds and providing data for the improvement of industrial drying equipment, this work aimed to calculate and evaluate the thermodynamic properties of moisture desorption of ryegrass seeds as a function of the equilibrium moisture content. Ryegrass seeds with initial moisture content of 10.4 (% d.b.) was used. The equilibrium moisture content of seeds was determined by static-gravimetric method at different temperatures (10, 20, 30, 40, and 50 °C) and water activity values (between 0.10 and 0.90), in three repetitions. The Chung Pfost model presented the best fit to the experimental data. It was observed that the integral isosteric desorption heat increased as the equilibrium moisture content decreased, ranged from 2499.95 to 4241.96 kJ kg-1 in the moisture content range 2.80 to 22.10 (% d.b.). Differential entropy also increased with decreasing equilibrium moisture content, as did Gibbs free energy, being positive for all temperature studied, indicating that ryegrass seeds desorption is a non-spontaneous process. The enthalpy-entropy compensation theory was satisfactorily applied to the sorption phenomenon, being controlled by enthalpy.

Temperature effects on chiral microemulsion electrokinetic chromatography employing the chiral surfactant dodecoxycarbonylvaline

Equilibrium water content and glistenings in acrylic intraocular lenses

As propriedades da água e sua relação com os componentes dos produtos agrícolas afetam os procedimentos pós-colheita, sendo estas relacionadas pelas isotermas de sorção.O modelo de Guggenheim-Anderson-de Boer (GAB) é usualmente utilizado para descrever as isotermas devido aos seus parâmetros relacionarem aspectos físicos do processo.Assim, objetivou-

The aim of this paper was to determine the moisture desorption isotherms and essentials thermodynamic properties of two Oak wood varieties. Desorption isotherms were measured using a static gravimetric method at 50, 60, 70 and 80 °C within the range of 5–90 % relative humidity. The equilibrium moisture content decreased with increasing temperature and decreased with decreasing relative humidity at a constant temperature. The ‘Thermodynamic’ sorption equation was found to be the best for describing the experimental moisture sorption isotherms of woods within the range of temperature and water activity investigated. The Fiber saturation point, deduced from the ‘Thermodynamic’ model parameters, depends on the temperature and varying from 22.6 to 54.4 (% kg water/kg dry matter). Isosteric heat of desorption and differential entropy were calculated by applying Clausius–Clapeyron equation to the desorption data fitted by the ‘Thermodynamic’ model. The isosteric heat of desorption and the differential entropy decreased with increasing moisture content according to an exponential law equation and varying from 2.03 to 31.14 kJ/mol and from 73.98 to 4.34 J/(mol K), respectively. The linear relationship between differential enthalpy and entropy satisfied the enthalpy–entropy compensation theory. The sign of Gibbs free energy was found to be positive (+283 J/mol) and (+97 J/mol) for Quercus robur and Quercus canariensis, respectively. The isokinetic temperature was found to be greater than the harmonic temperature. Based on the enthalpy–entropy compensation theory, it could be concluded that the moisture desorption isotherm of Oak wood is a non-spontaneous and enthalpy-controlled process.

Background: Sugarcane is one of the world’s largest crop. It grows in the tropical and subtropical regions, and its harvest provides 80% of the world’s sugar. In Latin America unrefined cane sugar is widely available and much less expensive than refined sugar. Sugarcane is a crop of great interest in Colombia due to the economic impact on the rural population and its application as sweetener agent. The poder of sugarcane (Saccharum officinarum L.) is widely used as a raw material in a wide range of industries such as foods, pharmaceutical, cosmetic and chemical. Objectives: The aim of the research work was the evaluation of the adsorption thermodynamics of sugarcane powder obtained by spray drying technology. Methods: The adsorption isotherms of sugarcane powder were evaluated at temperatures of 4 ± 0.1, 20 ± 0.2 and 30 ± 0.3 °C and its thermodynamic properties such as Gibbs free energy (G), differential heat of adsorption (ΔH) and differential entropy (ΔS) were calculated as a function of moisture content. Experimental data of adsorption isotherms were fitted to the GAB (Guggenheim – Andersen - de Boer), BET (Brunauer – Emmett - Teller), Henderson, Caurie, Smith, Hasley, Peleg, and Oswin models. Results: The results showed a type-II sigmoidal behavior, with temperature having a statistically significant effect. The GAB equation showed a better fit to the experimental data modeling (0.11≤aw≤0.87) although all models showed validity and goodness of fit to the experimental data. The net isosteric heat increased to a maximum value (57 kJ mol-1) and then decreased with the increase in moisture content. Conclusions: The sugarcane powder with maltodextrin, obtained by spray drying got low adsorption thermodynamic stability, as it required very low energy to occur this phenomenon, being obtained the maximum net isosteric heat when moisture content of 4.7% (d.b). This value is within the range of the monolayer moisture content found in the GAB and BET models.

Agglomeration of durum wheat semolina: Thermodynamic approaches for hydration properties measurements

SummaryThe aim of our work was to measure sorption isotherms on freeze-dried and convectively-dried fruits (apple cv. Idared; sour cherry cv. English Morello; blackcurrant cv. Tiben), previously osmotically dehydrated in fructo-oligosaccharide solution, or concentrated apple juice. Isotherms were fitted using the Guggenheim-Anderson-de Boer Model. In none of the cases studied was isotherm non-continuity in the vicinity of the initial value of aw observed. All isotherms, classified as type III, demonstrated an increase in the equilibrium water content, along with an increase in water activity. A higher water content was observed in lyophilised material compared to material dried by convection. The water content in the monolayer (100 g−1 dry matter) ranged from 12.0 g for dried apple, to 17.0 g for dried sour cherry. These values can be considered as optimal in order to ensure safe storage conditions. The dried fruits should therefore be kept in a water activity range of 0.45 – 0.54 for lyophilised, and 0.46 – 0.63 for convectively-dried material.